Not Applicable
Not Applicable
The invention relates to an apparatus for measuring the diameter and out-of-roundness of elongate workpieces, particularly those of round products advanced in their longitudinal direction in rolling mill trains, and processes for measuring the diameter and out-of-roundness of such workpieces.
It is known to perform the adjustment of the roll nip for flat products (heavy plates, hot-rolled hoops) in rolling mills via a closed regulation system. To this end, the last roll stand has arranged behind it a measuring system which continuously measures the thickness and, if necessary, the planarity of the rolled product and, thus, provides the actual value for the regulation system, which will then adjust the height of the roll nip and the geometry of the roll nip via appropriate actors with a view to maintaining the dimensional accuracy and flatness of the product.
It is contemplated to apply closed regulation systems to rolling mill trains for round products as well. From EP 0 800 43 156 A 2, it has become known to use a shadow measuring system including three measuring systems disposed under different angles. The measuring systems are pivoted in their positions in order to measure the diameter from varying directions.
The known apparatus and the process for measuring the diameter and out-of-roundness furnish imprecisely measured values if so-called xe2x80x9corbiform-curvedxe2x80x9d contours occur. xe2x80x9cOrbiform-curvedxe2x80x9d contours distinguish themselves by their property of being equal or approximately equal in their diameter values if their diameters are measured from different angles. Thus, their shadows also are equal in width. This missing difference or, at the most, this small difference between the largest and smallest diameters makes one believe that the workpiece being measured is of a very small out-of-roundness. This one, however, may actually prove to range far outside the admissible tolerances and requires to be reliably recognized by a measuring system.
It is the object of the invention to provide an apparatus and process for measuring the diameter and out-of-roundness, which allows of a quick and reliable measurement on workpieces by using a simple means.
The apparatus has three or more laser triangulation devices. The triangulation measures the distance of the workpiece surface from the triangulation device. Measurement is effected in a joint plane which is perpendicular to the longitudinal direction of the workpiece so that all triangulation devices perform a measurement along the circumference of the workpiece. In addition, the laser triangulation devices are arranged at angular spacings which are substantially equal two by two. This angle will be about 120xc2x0 if three laser triangulation devices are used whereas it will be reduced to 90xc2x0 and 72xc2x0 if four and five laser triangulation devices are used, respectively. The laser triangulation devices are directed in such a way that their laser beams will meet at a common point of intersection. The common point of laser beam intersection corresponds to the workpiece centre during the measuring operation. The direction of the laser triangulation devices helps achieve that each laser triangulation device not only measures any distance between the surface and the triangulation device, but that the radius of the workpiece may be associated with this distance value along the laser beam direction. Measuring the radius of the workpiece at three or more points makes it possible to recognize the out-of-roundness of the workpiece quickly and reliably even in case of xe2x80x9corbiform-curvedxe2x80x9d contours.
In an advantageous aspect of the apparatus, six laser triangulation devices are provided which enclose an angle of 60xc2x0 two by two. Generally, it is a fact that the number of measuring points increases with an increase in the number of triangulation devices and, thus, both the accuracy and speed of measurement is improved.
In order to achieve more measuring points at a given number of laser triangulation devices the laser triangulation devices are designed to be rotated about their point of intersection in the plane spanned by the laser beams. Thus, pivoting the laser triangulation devices enables the workpiece to be measured from different directions. The pivoting range is advantageously limited to the angular distance between the triangulation devices so that if the number of triangulation devices increases the pivoting range will decrease, and so will the speed in measuring, which is an advantage particularly for rapidly advanced workpieces.
The inventive apparatus has three or more laser scanners. Each laser scanner has a light-sensitive sensor with a laser which is directed thereto for illumination in the sensor area. The laser beams of the laser scanner are arranged around the workpiece in a triangle or polygon for sensing the workpiece tangentially. For example, if the apparatus has three laser scanners their laser beams form a triangle which is arranged around the workpiece. The triangle is dimensioned here in such a way that the workpiece partly hides the illuminated areas of the sensors. Thus, a workpiece outer edge casts a shadow onto the sensor where the shadow permits to determine the outer edge extending farthest into the laser beam. The advantage of this apparatus is that the position of the workpiece is arbitrary to a large extent. As long as the workpiece is arranged within the triangle and casts a shadow onto all sensors the position of the workpiece centre is arbitrary.
In another advantageous aspect of the invention, the three laser scanners are arranged in such a way that they span an equiangular triangle around the workpiece. Using three laser scanners also makes it possible here to recognize xe2x80x9corbiform-curvedxe2x80x9d contours quickly and reliably by using few measured values.
In a further advantageous aspect of the invention, each laser scanner has associated therewith a zero relative to which the distance of the workpiece outer edge extending farthest into the laser beam is measured with the laser scanners being disposed in such a way that their zeroes coincide in one point. Because of this arrangement of the laser scanners, each laser scanner measures the distance of the shadow-producing workpiece outer edge from a zero. If this zero coincides with the workpiece centre the distance determined from the shadow corresponds to the workpiece radius in the point of contact of the straight line.
In order to take different measured points as simply as possible the laser scanners are rotatably supported about the common zero.
In a further advantageous aspect of the invention, the workpiece is illuminated by the laser beam of the laser scanner in such a way that the workpiece casts a shadow which completely is within the illuminated sensor area. As compared to the above-described apparatus, one laser scanner determines two parallel straight lines here which reflect the maximal distance between two workpiece outer edges on opposed sides. The arrangement involving three or more laser scanners at angular distances which are approximately equal, i.e. 120xc2x0, 90xc2x0, 72xc2x0, etc., forms three or more pairs of parallel straight lines which contact the workpiece. These straight lines make it possible to determine the diameter and out-of-roundness of the workpiece independently of the location of its centre. A displacement of the centre may be established by a calculation forming a difference from the data measured.
In a further advantageous aspect of the invention, this one is rotatably disposed in the plane spanned by the laser beams.
In a further advantageous aspect of the invention, it uses laser triangulation devices, which are directed to the workpiece in such a way that measuring the surface furnishes the workpiece radius in the point of contact.
The second measuring process is performed by using 3 or more laser scanners wherein one or two straight lines bearing on the outer edge, which extend in parallel with the laser beam, i.e. in the laser beam direction, are determined for each laser scanner from the shadow of the workpiece in a first process step. The appearance of one or two workpiece shadow edges on the sensor is dependent on whether the laser scanner merely illuminates the workpiece tangentially or illuminates the sensor so completely across a width that the workpiece casts a full shadow within the illuminated sensor area. In a second process step, an evaluation device computes a circle, which bears on the straight line as a tangent line, from three determined straight lines each. In the process steps which succeed here, the measuring operation to cpmoute the circle is repeated several times and the diameter and out-of-roundness of the workpiece is determined from the circle diameters measured.
In a further advantageous aspect of the process, the laser scanners are turned around the workpiece when the measurement is repeated. Thus, a major number of measured values is produced which allow to determine the out-of-roundness better within a short time.
Preferably, the measurement by the laser scanners is performed in a synchronized manner in response to a trigger signal. The synchronous measurement ensures that a radial motion of the workpiece during the measurement does not lead to any falsification of the results measured.
In a further advantageous aspect of the invention, the laser scanners measure the workpiece at most varied times and the evaluation device determines a motion vector for the workpiece from the times and the respective values measured. Since the evaluation device is capable of considering both the values measured and the time thereof it is possible to recognize and compensate a motion of the workpiece between the measuring operations.
In an appropriate aspect of the process, if more than three non-parallel straight lines have been determined, all triplets of straight lines are used for a calculation of the circle. If the number of straight lines is adequate it will also be possible to reconstruct a section of the surface contour with the aid of a computer so that it is possible to precisely determine the local out-of-roundness.